High-temperature-driven degradation analysis and modelling of an industrial gas turbine applicable γ/β NiCoCrAlYRe coating– Part II: Diffusion modelling and experimental validation under isothermal conditions

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In a two-part research, the degradation process of a commercially utilised NiCoCrAlYRe coating on an IN738LC substrate was both simulated and experimentally validated. The first part of the study delved into the microstructural characteristics of the overlay coating system and analysed the oxidation and interdiffusion mechanisms. This second part extends the analysis to simulations of the coating degradation at temperatures of 900 °C and 1000 °C.The interdiffusion between the substrate and coating was modelled utilising thermodynamic and kinetic mobility data, while the oxidation aspect was addressed using two different established models from Whittle and Meier et al., along with an adapted approach specifically tailored for MCrAlY overlay coatings devised in this research. The simulation results were validated experimentally for up to 7000 h, with the degradation state evaluated based on the depletion of β-NiAl in the coating.Good agreement was found between simulated and experimental data. The initial coating and substrate microstructures were sufficiently predicted based on thermodynamic data, and the simulations closely matched the observed degradation pattern. The most precise alignment between simulated and experimental β-NiAl depletion was achieved with the newly proposed oxidation modelling approach for MCrAlY systems. While more optimisation is required to accurately predict the precipitation of chromium phases and carbides and to account for interdiffusion-obstructing effects, particularly at 1000 °C, the results demonstrate the potential of thermodynamic-kinetic modelling for estimating the lifespan of MCrAlY systems under diffusion-driven degradation conditions.